Venetian blinds, pleated blinds, cellular blinds, and some Roman shades have a headrail, a bottom rail, window covering material extending between the headrail and the bottom rail and lift cords extending from the headrail to the bottom rail. The bottom rail may be rectangular and have a height as small as one half inch and as large as two inches. Some bottom rails have a curved front face or a curved bottom. Other bottom rails are cylindrical. Typically, one end of each lift cord is attached to and wound on a spool in the headrail and the opposite end of the lift cord is attached to the bottom rail. The spools on which the lift cords are wound may be on a common shaft that is operated by a pull cord or a cord loop. In cordless blinds there are spring motors which provide the force for winding the spools that contain the lift cords. U.S. Pat. No. 5,482,100 to Kuhar discloses a cordless, balanced Venetian blind or shade with consistent variable force spring motor. This system uses spring motors to balance the weight of the bottom rail and the accumulating window covering material as the window covering is raised or lowered by simply grasping the bottom rail and urging it upwardly or downwardly.
A problem common among window coverings having a bottom rail is balancing of the bottom rail so that it is level when the window covering material is at a fully lowered or partially lowered position. In many window coverings the lift cord extends through a hole in the bottom rail and is held in place by a knot tied in the lift cord. When the window covering is installed the installer can level the bottom rail by changing the location of the knot on selected lift cords. In other window coverings a clamp in provided in the bottom rail for attaching the lift cord to the bottom rail. In this product the installer can lengthen or shorten the lift cord by unclamping, moving and re-clamping the lift cord.
Many window coverings have weights in the bottom rail that can be moved left or right on the bottom rail. Because the lift cords are usually polyester adding weight to or shifting weight on the bottom rail will stretch the lift cord and thus can be used to level the bottom rail. One easy method to level a bottom rail is to use weighted, tape-like strips which are adhered to the bottom rail by the fabricator at appropriate locations. Most frequently, such strips are applied after the window covering has been fabricated and after it has been determined where any imbalance may exist. Another approach for resolving the weight balance issue is disclosed by Colson et al. in U.S. Pat. No. 5,320,154. They teach a weight element that is slidably disposed in the bottom rail and is moved longitudinally along the bottom rail until appropriate balance is achieved. U.S. Pat. No. 6,769,471 to Voss et al. discloses another approach to using weights to level a bottom rail.
While all of these approaches provide methods for achieving a level bottom rail, they suffer from one or more drawbacks with regard to installation and/or use. First, none of these systems are easy for a consumer to use and some require the use of specialized tools. Second the balance of the bottom rail may change after the window covering has been hung because the window covering material or the a cord may have stretched or contracted unevenly along its length causing one end of the bottom rail to be lower than the other end. Should that occur it may be necessary to dismantle the bottom rail and readjust the cord length or the weight and balancing system. Even if the weights on the bottom rail are easily accessible, repositioning those weights to level the bottom rail may be difficult, depending on the skill of the owner or user of the window covering.
Consequently there is a need for a bottom rail which is easy to level, not only at the time of installation but also after the blind has been hung in place for several months or even years.
There is also a need for a bottom rail level adjusting device which can be used on the bottom rails which are currently in use. Indeed, such a bottom rail level adjustor should be capable of being retro-fitted on existing blinds.